clk: mediatek: mt7988-infracfg: fix clocks for 2nd PCIe port

Due to what seems to be an undocumented oddity in MediaTek's MT7988
SoC design the CLK_INFRA_PCIE_PERI_26M_CK_P2 clock requires
CLK_INFRA_PCIE_PERI_26M_CK_P3 to be enabled.

This currently leads to PCIe port 2 not working in Linux.

Reflect the apparent relationship in the clk driver to make sure PCIe
port 2 of the MT7988 SoC works.

Fixes: 4b471943

 ("clk: mediatek: add drivers for MT7988 SoC")
Suggested-by: Sam Shih <sam.shih@mediatek.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://lore.kernel.org/r/1da2506a51f970706bf4ec9509dd04e0471065e5.1710367453.git.daniel@makrotopia.org
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>